**3. Bioaccumulation of insecticides and their transfer in the food chain**

As from the middle of the twentieth century, human health and the natural environment have begun to be adversely affected upon the excessive use of pesticides, including insecticides. These substances, which are used against insects that

**Figure 2.** *Bioaccumulation of insecticide residues in the food chain [9].*

harm agricultural products in the beginning, have indeed brought about significant increases in the quality and quantity of agricultural products. Insecticides, which serve to protect agricultural products by destroying unwanted insects, have provided great benefits for both the environment and public health by also controlling pathogenic vectors. However, as a result of excessive use of these substances to obtain better quality and more products later on, many unexpected harmful effects have been experienced. These substances remain intact for a long time in water, soil, fruits and vegetables and cause environmental pollution. Since insecticides applied to agricultural products can remain intact for a long time, they can reach the food chain by mixing with soil and water, and then passing through plants and animals [11–13]. These pollutants enter through the skin, gills, and digestive systems of aquatic organisms and begin to accumulate in the organs of these living creatures. These pollutants entering the body are metabolized and excreted with the help of body fluids. If they cannot be excreted from the body, they accumulate in tissues with high fat content and may remain in these tissues for many years [13, 14]. The accumulation increases exponentially when small aquatic organisms carrying insecticide residues are eaten by larger aquatic organisms and plants with insecticide residues are eaten by animals. Thus, the residue level in humans, who are in the last link of the food chain, becomes much higher and concentrated [11, 12]. The bioaccumulation of pesticide residues in the food chain is shown in **Figure 2** [9].
